Due to its superior electrical and optical properties, such as high carrier mobility and gapless band structure, graphene has been considered as a promising material to replace existing photoactive semiconductor materials for high speed, high sensitivity and broadband photo detection. See Xia F N, Mueller T, Lin Y M, Valdes-Garcia A, Avouris P., Ultrafast graphene photodetector. Nat Nanotechnol 4, 839-843 (2009) (hereinafter referred to as “Xia”) and Nair R R, et al., Fine structure constant defines visual transparency of graphene. Science 320, 1308-1308 (2008) (hereinafter referred to as “Nair”), both of which are incorporated herein in their entirety. The photo response in a graphene-based photodetector is mainly attributed to three mechanisms: (i) the photovoltaic effect, (ii) the photothermoelectric effect, and (iii) the photogating effect. See Lemme M C, et al., Gate-Activated Photoresponse in a Graphene p-n Junction. Nano Lett 11, 4134-4137 (2011) (hereinafter referred to as “Lemme”); Mueller T, Xia F N A, Avouris P. Graphene photodetectors for high-speed optical communications. Nat Photonics 4, 297-301 (2010) (“Mueller”); Gabor N M, et al., Hot Carrier-Assisted Intrinsic Photoresponse in Graphene. Science 334, 648-652 (2011) (hereinafter referred to as “Gabor”); Sun D, et al., Ultrafast hot-carrier-dominated photocurrent in graphene. Nat Nanotechnol 7, 114-118 (2012) (hereinafter referred to as “Sun”); Tielrooij K J, et al., Generation of photovoltage in graphene on a femtosecond timescale through efficient carrier heating. Nat Nano 10, 437-443 (2015) (hereinafter referred to as “Tielrooij”); Konstantatos G, et al., Hybrid graphene-quantum dot phototransistors with ultrahigh gain. Nat Nanotechnol 7, 363-368 (2012) (hereinafter referred to as “Konstantatos”); and Zhang D Y, Gan L, Cao Y, Wang Q, Qi L M, Guo X F., Understanding Charge Transfer at PbS-Decorated Graphene Surfaces toward a Tunable Photosensor (hereinafter referred to as “Zhang”), all of which are incorporated herein in their entirety.
In addition to enhanced sensitivity, wavelength selectivity is a desirable characteristic for photodetector in certain applications. The spectral selectivity is determined by integrating microcavity, waveguide or metal plasmonic structures. See, Furchi M, et al., Microcavity-Integrated Graphene Photodetector. Nano Lett 12, 2773-2777 (2012) (hereinafter referred to as “Furchi”); Gan X T, et al., Chip-integrated ultrafast graphene photodetector with high responsivity. Nat Photonics 7, 883-887 (2013) (hereinafter referred to as “Gan”); and Echtermeyer T J, et al., Strong plasmonic enhancement of photovoltage in graphene. Nat Commun 2, (2011) (hereinafter referred to as “Echtemeyer”), all of which are incorporated herein in their entirety. Although, as in metal plasmonic structures, the intrinsic plasmonic absorption in graphene nanostructures is primarily determined by their geometry, the low density of states promises graphene the potential of tuning the light absorption by electrostatic gating. See, Freitag M, Low T, Zhu W J, Yan H G, Xia F N, Avouris P, Photocurrent in graphene harnessed by tunable intrinsic plasmons. Nat Commun 4, (2013) (hereinafter referred to as “Freitag”) and Chen J N, et al., Optical nano-imaging of gate-tunable graphene plasmons. Nature 487, 77-81 (2012) (hereinafter referred to as “Chen 2”), both of which are incorporated herein in their entirety. However, in addition to the high cost associated with a nanofabrication process, all of these photodetectors rely on the intrinsic photo response of graphene, leading to a low responsivity of <1 A·W−1, which limits its potential applications. It is well known that the silicon oxide layer on silicon wafer can serve as a Fabry-Perot cavity, which is responsible for the optical visibility of single layer graphene. Abergel D S L, Russell A, Fal'ko V I, Visibility of graphene flakes on a dielectric substrate. Applied Physics Letters 91, 063125 (2007) (hereinafter referred to as “Abergel”) and Roddaro S, Pingue P, Piazza V, Pellegrini V, Beltram F, The Optical Visibility of Graphene: Interference Colors of Ultrathin Graphite on SiO2. Nano Lett 7, 2707-2710 (2007) hereinafter referred to as (“Roddaro”), both of which are incorporated herein in their entirety.